Process for high efficiency hot isostatic pressing

ABSTRACT

A process for high efficiency hot isostatic pressing in a hot isostatic pressing treatment for sintering or densifying a ceramic or metallic work in a high temperature and high pressure gas atmosphere, comprising preheating the work outside a high pressure vessel prior to the hot isostatic pressing treatment, transferring the preheated work as surrounded with the gas in a hot state into the high pressure vessel, then treating the work at high temperature and high pressure in a gas atmosphere, thereafter taking out the work from the high pressure vessel together with the gas atmosphere, then cooling the work if necessary, and subsequently taking it out from the gas atmosphere, as well as an apparatus for practicing the above process, wherein a treating chamber for effecting the hot isostatic pressing treatment is covered with a hermetic casing, and at least one valve mechanism capable of providing communication and cut-off between the interior and exterior of the treating chamber is provided in each of upper and lower portions of the treating chamber.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an improvement of modular type hotisostatic pressing (hereinafter referred to as "HIP") method andapparatus provided with preheating or cooling auxiliary stations forsintering or densifying ceramic or metallic powder at high temperatureand pressure in an inert gas atmosphere to obtain a molded producthaving a dense texture of a nearly true density.

(2) Description of the Prior Art

The HIP treatment has recently been specially noted in various fields asa superior method for compressing a work isotropically at a hightemperature using an inert gas as a pressure medium to produce a densesinter from ceramic powder, metallic powder, or a mixture thereof, orfor removing residual cavities in cemented carbides by squeezing, or fordiffusion-bonding of metallic materials.

According to the HIP method, there can be obtained various advantagessuch as, for example, high densification at low temperatures, obtainingof a dense and uniform texture having a density close to a theoreticalvalue, improvement of mechanical and physical properties of powder,molding of powder unsuitable for molding, producing of large-sizedproducts not restricted by the capacity of a press as in ordinarymolding presses, molding of various composite materials such as metalsand ceramics, and improvement of the material yield. By the HIPtreatment, moreover, internal defects of an object can be removed, andthe toughness and deflective strength can be enhanced, so methods whichutilize this effect have been proposed other than the above-mentionedpowder molding and sintering, such as improvement of the performance ofsintered tool material, etc. and diffusion-bonding of the turbine bladeand body by HIP to obtain extremely strong bonding.

Since such HIP treatment is performed in an atmosphere of hightemperature and pressure, it is necessary to use an HIP furnace of aspecial structure, and a long period of time is required for executingthe operation cycle comprising raising the temperature, raising thepressure, maintaining the elevated temperature and pressure, loweringthe temperature and lowering the pressure. Therefore, shortening thiscycle time and thereby improving the efficiency has been an importanttechnical problem.

In a effort to solve the above-mentioned problem, various attempts havebeen made for improving the utilization efficiency per unit time of theHIP furnace by performing heating in a preheating furnace to raisetemperature which requires a long period of time and performing in theHIP furnace only the raising of the pressure and/or raising thetemperature to a slight extent. A typical example is the apparatusproposed in the specification of British Patent No. 1,291,459. However,this proposed apparatus is disadvantageous in that the equipment cost isincreased because a preheating furnace is needed in addition to theordinary HIP furnace although the shortening of the cycle time isattained, in that the heat loss caused by heat radiation from the workis very large because the conveyance of the work after preheating isperformed in the air, and in that when the high-temperature work afterpreheating is charged into the HIP furnace, the lower inner wall surfaceof the furnace is overheated and the lower seal ring is easily damagedthereby, which is a serious problem.

In this type of apparatus for which safety is strictly required, theadoption of the above-mentioned apparatus is very problematic even ifthe shortening to the cycle time is attained.

As the material of heating element used in the heater, usually anelectric heater, in the HIP furnace, there has been proposed Fe-Al-Cr,molybdenum of graphite. Among these materials, Fe-Al-Cr, which isresistant to oxidation at high temperatures, has been evaluated as theonly material capable of being released to the air at a hightemperature, but the temperature at which this material can be usedstably is up to about 1,100° C.

On the other hand, molybdenum- or graphite-based materials which arestably employable at above 1,100° C. are severely oxidized at hightemperatures, so cannot safely be exposed to the air unless thetemperature range is below about 200°-300° C. Therefore, a long periodof time is required for lowering the temperature to below 300° C.although the lowering of pressure can be done in a relatively short timeperiod after performing the HIP treatment at a temperature as high asone thousand and several hundred degrees centigrade in a high pressureinert gas atmosphere. Thus, the long period of time required fromopening the HIP furnace until taking out of the work greatly impedesefficient utilization of the apparatus. As an example, according to acertain conventional typical pattern in the HIP treatment, the timerequired for each treating step is as follows:

    ______________________________________                                                             Time required                                            Step                   hr.     min.                                           ______________________________________                                        Loading of workpiece   0.      10                                             Vacuum suction, Gas replacing                                                                        1.      00                                             Raising temp., Raising pressure                                                                      3.      00                                             Maintaining elevated temp. and pressure                                                              2.      00                                             Lowering temp.         8.      00                                             Recovery under reduced pressure                                                                      1.      00                                             Taking out of workpiece                                                                              0.      10                                             Total                  15.     20                                             ______________________________________                                    

By the foregoing preheating, the 3 hours' temperature and pressureraising time is shortened to about 1 hour and 40 minutes, correspondingto only an 8.7% reduction of the cycle time, that is, the time requiredfor lowering temperature, which occupies the greater part of the cycletime, still remains as a serious efficiency impeding factor.

For shortening the time required for lowering temperature, it has beenpreviously attempted to perform cooling by providing a coolant jacketaround the outer periphery of the HIP furnace and utilizing, in loweringthe temperature, convection of gas induced by the difference between thespecific gravity (small) of the high temperature gas at the furnacecentral portion and the specific gravity (large) of the low temperaturegas in contact with the furnace inner wall, as disclosed, for example,in the specification of U.S. Pat. No. 4,217,087 and Japanese PatentPublication No. 8689/1973. According to such method, however, thecooling capacity deteriorates to a large extent with a decrease of thetemperature difference between the high temperature gas and the lowtemperature gas. Therefore, the temperature lowering rate becomessmaller as cooling advances, and as a result, it is impossible to expecta remarkable shortening of the time required until reaching thetemperature at which the HIP furnace can be opened.

In such technical level, the applicant of the present invention haspreviously proposed (see Japanese Patent Laid Open Publication No.71301/1983) and HIP system capable of shortening the cycle time withoutexerting a bad influence on its components and having a high safety, aswell as a method capable of improving the working efficiency remarkablyby using such system. This proposed HIP system, called a modular typeHIP system, comprises an HIP furnace, a plurality of auxiliary stations,the HIP apparatus and the auxiliary stations being disposed side by sidealong and above a horizontally laid track, and a carriage for travellingon the track. The HIP apparatus consists mainly of a high pressurevessel and a treating chamber and is provided with means for supply anddischarge of an atmospheric gas for applying HIP treatment to aworkpiece loaded into the treating chamber and is also provided withmeans for adjusting pressure and temperature, the high pressure vesselcomprising a pressure-resistant vertical cylinder having a closed topremovably fitted in the bottom of the cylinder, the treating chamberbeing enclosed with an inverted cup-like heat insulating barrier whichbarrier is mounted on the upper surface of the barrier and is internallyprovided with a heater. Each of the auxiliary stations mainly comprisesa dome-like vessel having a size which permits the treating chamber tobe completely enclosed therein, also having a bottom opening whichpermits the above plug to be fitted therein, and further having acoolant jacket provided around the outer periphery thereof. Eachauxiliary station is also provided with the heater enclosed thereintogether with the treating chamber, means for supply and discharge of anatmosphere gas for heating or cooling the workpiece and temperatureadjusting means.

Thereafter, the applicant of the present invention has made variousimprovements on the above-proposed apparatus and filed the thus-improvedapparatus (see Japanese Utility Model Laid Open Publication Nos.157,300/1983 and 54098/1984). According to these devices, in theforegoing modular type HIP system, a single valve mechanism is providedin the upper or lower portion of a casing which houses the treatingchamber. This valve mechanism is opened when the treating chamber isinserted into the HIP furnace or an auxiliary station, to therebyprovide communication between the interior and exterior of the treatingchamber, and it is closed when the treating chamber is taken out.According to this construction, it is possible to take out the workpiecewhich has been preheated in the auxiliary station, from the auxiliarystation integrally with the treating chamber together with the inertatmospheric gas, convey and load the workpiece into the HIP furnace,then after HIP treatment and upon dropping of pressure, taken out theworkpiece from the HIP furnace integrally with the treating camberimmediately without waiting for such becoming cold, and cool it in anauxiliary station. Thus, a remarkable shortening of the cycle time inthe HIP treatment and a great improvement of the working efficiencycould be attained. In these devices, however, since the casing whichhermetically encloses the treating chamber is taken out from the HIPfurnace also under a state of high temperature, there arises theforegoing serious problem that the seal ring attached to the lowerportion of the high pressure vessel is easily damaged when opening theHIP furnace in a still hot condition of its interior and taking out thetreating chamber held at a high temperature.

SUMMARY OF THE INVENTION

The present inventors have carefully reviewed the foregoing prior artand studied about the method of ensuring an efficient and safe operationof the entire system while making the most of the advantages of themodular type and without impairing the utilization efficiency of the HIPfurnace. As a result, the present inventors have been able to solve allof the conventional problems by cooling the work rapidly to anappropriate temperature in the HIP furnace after HIP treatment, and havethus reached the present invention.

As an apparatus employable for practicing such method of the presentinvention, there is provided according to the invention an apparatuscharacterized in that, in an HIP furnace consisting mainly of a highpressure vessel comprising a pressure-resistant vertical cylinder havingone closed end and a plug removably fitted closely in an opening portionat the other end of the cylinder, and a treating chamber surrounded witha heat insulating barrier and capable of being attached to and detachedfrom the high pressure vessel together with a workpiece loaded therein,the heat insulating barrier being attached to and detached from the highpressure vessel together with a workpiece loaded therein, the heatinsulating barrier being internally provided with a heater. The HIPfurnace is further provided with a gas supply and discharge means forsubjecting the workpiece to a predetermined high temperature and highpressure treatment in a gas atmosphere. The auxiliary stations are eachconstituted mainly of a vertically oriented cylinder capable ofenclosing therein the treating chamber hermetically, and provided with agas supply and discharge means. The carrier device is for carrying thetreating chamber together with the workpiece between the HIP furnace andeach auxiliary station and loading and loading it to and from eachvertical cylinder. In such HIP system, said treating chamber is coveredhermetically with a casing and at least one valve mechanism capable ofproviding communication or cut-off between the interior and exterior ofthe treating chamber is provided in each of upper and lower portions ofthe treating chamber.

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a modular type HIP system embodying thepresent invention;

FIGS. 2 to 5 are schematic views showing structures and operations ofvarious portions in FIG. 1, of which FIG. 2 is a schematic view of atreating chamber, FIG. 3 is a schematic view of the treating chamber asreceived in an auxiliary chamber, FIG. 4 is a schematic view of thetreating chamber as received in an HIP furnace and under HIP treatment,and FIG. 5 is a schematic view of the treating chamber under rapidcooling in the HIP furnace; and

FIG. 6 is a schematic view of an HIP apparatus according to a modifiedembodiment of the present invention.

The method and apparatus of the present invention will be described indetail hereinunder with reference to the accompanying drawings.

FIG. 1 is a schematic explanatory view showing a positional relationbetween an HIP furnace and auxiliary stations in a modular type HIPsystem according to an embodiment of the present invention, in which acarriage 2 is mounted for travelling on a track 1, and on the carriage 2is mounted a support table 3 capable of being vertically moved by aknown or commonly used drive means (not shown) such as, for example, achain wind-up type, worm gear and rack type, or piston type drive means.Above and along the track 1 are disposed side by side a plurality ofauxiliary stations 4, 4', . . . and an HIP furnace 5. The HIP furnace 5is constructed mainly of a high pressure vessel comprising a vertical,pressure-resistant cylinder 7 having a top portion closed hermeticallywith an upper plug 6 and a lower plug 8 capable of being fitted in thebottom of the cylinder 7 hermetically and removably, and a treatingchamber 11 surrounded with an inverted cup-like heat insulating barrier10 which is mounted on the upper surface of the lower plug 8 andenclosed in the high pressure chamber and which is internally providedwith a heater. The treating chamber 11 can be removed to the exterior ofthe HIP furnace 5 by removing the heat insulating barrier 10 and thelower plug 8 together from the pressure-resistant cylinder 7. On theother hand, the auxiliary stations 4, 4', . . . mainly comprise verticalcylinders 13, 13', . . . and they each have capacity and size sufficientto completely enclose therein the treating chamber 11. The bottomopening of each of the vertical cylinders 13, 13', . . . has size shapewhich permit the lower plug 8 to be fitted therein.

The treating chamber 11, which is mounted on the support table 3 of thecarriage 2, can be positioned just under the vertical,pressure-resistant cylinder 7 or any of the vertical cylinders 13, 13',. . . by travelling of the carriage 2, and can be inserted into orremoved from the vertical cylinder 7, 13, or 13' in that position byoperation of a lift means. A press frame 14 for grippingly supportingthe upper plug 6 and the lower plug 8 is mounted on a carriage 15 andcan travel on the track 1 and reciprocate between operating andretracted positions. The illustrated construction of the press frame 14a mere example, and various modifications thereto may be made. Forexample, such may be hinged to a vertical fixed shaft and reciprocatedbetween operating and retracted positions by a pivotal motion thereof.

FIG. 2 is a schematic vertical section of the treating chamber 11 as aconstituent member of the system of FIG. 1, in which a heat insulatingbarrier 10 internally provided with a heater 9 comprising an electricheating plate in an electrically insulated state is mounted on the uppersurface of the lower plug 8. The power supply to the heater 9 iseffected through a power lead wire (not shown) which is attached to thelower plug 8 in an electrically insulated and hermetically sealedcondition. The heat insulating barrier 10 surrounding the treatingchamber 11, including the heater 9, is formed of a heat-resistantfibrous heat insulator such as ceramic fiber filled betweensubstantially concentric inverted cup-like hermetic casings 16 and 17formed of a gas impermeable material. The heat insulating barrier 10 isgas permeable and it is mounted removably on the upper surface of thelower plug 8.

The heat insulating barrier 10 and the treating chamber 11 are incommunication with each other through a through hole 18 formed in partof the hermetic casing 16. The upper surface of the lower plug 8 iscovered with a heat insulating seat 19 of a similar structure to theheat insulating barrier 10, and a hermetic casing 20 which forms anouter periphery of the heat insulating seat 19 is also formed with athrough hole 21 to provide communication between the seat 19 and thetreating chamber 11.

Further, the greatest feature of the present invention resides in thatat least one valve mechanism is provided in each of upper and lowerportions of the treating chamber 11 thereby permitting communication andcut-off between the interior and exterior of the treating chamber 11. Inthe illustrated embodiment, one valve mechanism 22 and one similarmechanism 23 are provided in the top of the hermetic casing 17 and inthe lower plug 8, respectively. But, it goes without saying that aplurality of such valve mechanisms may be provided in each of thoseportions.

The valve mechanism 22 comprises a valve 25 for opening and closing avalve hole 24 formed in the top of the hermetic casing 17 from thetreating chamber 11 side, a stem 26 contiguous to the valve 25 andinserted slidably in the valve hole 24, and a flange 27 and the hermeticcasing 17 is interposed a spring 28, and the step 26 is urged upward bythe biasing force of the spring 28. In the lower valve mechanism 23,which is of about the same structure as above, a seal ring 29 isdisposed in an intermediate portion of a valve bore 24' to preventcommunication of the treating chamber 11 with the outside air when avalve 25' is opened. The diameter of the valve bore portion above theseal ring 29 is made a little larger than the outside diameter of a stem26' to form an annular hole 30, and the treating chamber 11 communicateswith an upper side space of the lower plug 8 through a conduction hole31 extending sideways from the annular hole 30. The valves 25 and 25'are opened by urging the respective flanges 27 and 27' against thebiasing force of springs 28 and 28' and are closed upon release of thebiasing force.

In the modular type HIP system of the invention having the aboveconstruction, the heat insulating barrier 10 is separated from the lowerplug 8 together with the hermetic casings 16 and 17 to open, thetreating chamber 11, then a workpiece 33 is put on a sample stand 32,and thereafter the heat insulating barrier 10 is fixed onto the lowerplug 8 to close the treating chamber 11. In this way, preparations arecompleted. The treating chamber 11 thus loaded with the workpiece 33 isthen inserted into the vertical cylinder 13 of the auxiliary station 4.

FIG. 3 is a schematic vertical section of the treating chamber 11 asreceived in the auxiliary station 4, in which a push rod 34 is providedin the top of the vertical cylinder 13 in a position coaxial with thevalve mechanism 22, and it is urged upward by the biasing force of aspring 36 which acts on an upper end flange 35, the push rod 34 beingmounted hermetically through a seal ring 37. Further, the verticalcylinder 13 is provided with a gas supply and discharge port 38 whichcommunicates with a vacuum exhaust system and a gas supply/dischargesystem (neither shown).

In such auxiliary station 4, the work 33 is first subjected to arequired heat treatment. For example, in vacuum sintering of a formedbody of powder, the flanges 27' and 35 are pushed by suitable means toopen the upper and lower valves 25 and 25', as shown in FIG. 3, then theheater 9 is charged with electricity while vacuum suction is performedthrough the gas supply and discharge port 38. Alternatively, afterreplacing the vacuum with an inert gas such as argon or nitrogen, theupper and lower valves 25 and 25' are closed to seal the inert gas inthe hermetic casing 17, thereby performing atmospheric sintering. In thecase of oxide type ceramics, there may be used a gaseous mixtureconsisting of an inert gas such as Ar or N₂ and a very small amount ofO₂.

After completion of the above heat treatment, and where the interior ofthe treating chamber 11 is vacuum, after replacing it with apredetermined gas, the lower plug 8 is removed from the lower opening ofthe vertical cylinder 13 together with the workpiece 33, treatingchamber 11 and hermetic casings 16 and 17, which are then transferred tothe HIP furnace in a hot state of the treating chamber 11 and insertedinto the furnace interior from the lower opening of the verticalpressure-resistant cylinder 7. During their transfer, both the upper andlower valves 25 and 25' are closed as shown in FIG. 2 and the interiorof the treating chamber 11 can be maintained with a predetermined gasatmosphere. Therefore, materials which are susceptible to oxidation atelevated temperatures despite being stably employable at elevatedtemperatures in a non-oxidative atmosphere can be used for the heatingelement, etc.

FIG. 4 is a schematic vertical section of the treating chamber 11 asreceived in the vertical pressure-resistant cylinder 7 of the HIPfurnace 5, in which the HIP furnace 5 comprises the cylinder 7 and theupper plug 6 which seals the upper end of the cylinder 7, with the lowerplug 8 being hermetically fitted in the lower end of the cylinder 7,thereby forming a high pressure chamber 39 in the interior of thecylinder.

In the upper plug 6 is formed a gas flow path or conduit 40 for supplyand discharge of a gaseous pressure medium. In the illustratedembodiments the vertical pressure-resistant cylinder 7 is supported andfixed by a support structure (not shown), and the upper and lower plugs6 and 8 are grippingly supported by the press frame 14 to prevent theirdisengagement during operation. The plugs may be fixed to thepressure-resistant cylinder by conventional means such as a threadedengagement, but the press frame gripping method is most recommended fromthe standpoint of ensuring safety in operation at high pressures.

In the apparatus of such structure, the treating chamber 11 whoseinterior is in a hot state is inserted into the verticalpressure-resistant cylinder 7 by fitting the lower plug 8 which carriesthereon the treating chamber 11 hermetically into the lower end of thecylinder 7. In this state, the valve 25 is opened and the valve 25'closed, and the gaseous pressure medium is introduced through theconduit 40 into the pressure chamber 39, while the heater 9 is chargedwith electricity to continue heating and raise the internal temperatureof the furnace thereby performing HIP treatment.

The pressurization is effected at a high pressure of at least about 500atm using a gaseous pressure medium comprising an inert gas such asargon or helium gas alone or in combination with a small amount ofoxygen, and as a high temperature is adopted sufficient to cause aplastic flow of the constituent material of the work such as ceramics ormetal, but in the method of the present invention, the temperature rangeof about 1,200°-2,000° C. is applied very effectively to the highefficiency and high temperature HIP treatment. By the HIP treatment, theworkpiece is more densified and there is obtained a formed body of ahigh density close to the theoretical density.

FIG. 5 is a schematic vertical section showing a forced cooling stepwhich is carried out in the HIP furnace after completion of the HIPtreatment. As shown in the figure, upon completion of the HIP treatment,the lower valve 25' is opened without reducing the pressure, and nowboth the upper and lower valves are open, whereby a circulating gasstream is created by convection of gas along the arrowed path in thefigure. More particularly, the gas in the high pressure chamber 39 whichhas been cooled in contact with the inner wall of the verticalpressure-resistant cylinder 7 goes downward, then passes through theconduction hole 31, annular hole 30 and through hole 21 and enters thetreating chamber 11, where it absorbs the interior heat, then passesthrough the through hole 18 and heat insulating barrier 10 and againflows into the high pressure chamber 39 from the valve hole 24 andradiates heat.

According to the conventional HIP method, not of a modular type, theinterior of the HIP furnace must be cooled to the temperature whichpermits opening to the outside air, namely, about 200° C. or lower, andas the temperature lowers, the lowering rate becomes smaller, asreflected in a long time of about 8 hours required for the temperaturelowering operation. After the adoption of a modular type HIP method, itbecame possible to perform only pressure reduction after HIP treatment,transfer the treating chamber as heated still hot to an auxiliarystation and cool it to a predetermined temperature in that station.However, since there scarcely occurs convection of gas in the vicinityof the atmospheric pressure, a long period of required for cooling, forexample, about 10 hours is required for lowering the temperature from600° C. to 300° C. Consequently, there arises the necessity ofincreasing the number of auxiliary stations sufficiently to improve theutilization efficiency of the HIP furnace, or various improvements areneeded for the forced cooling in auxiliary stations, thus leading toincrease of the equipment cost. Additionally, the seal ring of the HIPfurnace is apt to be damaged because the treating chamber as heated hotis taken out, and this is a serious problem.

On the other hand, according to the foregoing method of the presentinvention, since cooling is done under high pressure after HIPtreatment, there occurs a vigorous convection of gas, whereby the heatis absorbed rapidly and the workpiece is cooled in a surprisingly shorttime. For example, in the case of argon held at a pressure as high as1,000 kg/cm², its viscosity is only 1.1 to 3 times that of argon gas atatmospheric pressure although the former has a density several hundredtimes that of the latter, so a slight temperature gradient would cause avigorous convection providing an extremely large value of convectiveheat conductivity, that is, the conduction efficiency from the workpieceto the intra-furnace atmosphere becomes very high. Actually, when thetemperature was lowered from 600° C. to 300° C. in a high pressure argongas atmosphere of 1,000 kg/cm², there was required only about one hour.

Preferably, the rapid cooling in the HIP furnace according to the methodof the present invention is carried out until the temperature of theworkpiece is not higher than about 300° C. After completion of thecooling step, the gaseous pressure medium is discharged from the conduit40 to let the internal pressure of the furnace revert to normalpressure, then the press frame 14 is removed and the lower plug 8 isremoved from the pressure-resistant cylinder 7 in a closed state of theupper and lower valves 25 and 25', then taken out from the HIP furnace 5together with the treating chamber 11 and the workpiece 33 loadedtherein and attached to the auxiliary station 4. In this case, since thetemperature of the hermetic casing 17 which encloses the treatingchamber 11 is also quite low, it is not possible at all that the sealrings and other portions of the vertical cylinders 7, 13 and 13' of theHIP furnace 5 and auxiliary stations 4, 4' will be badly influencedduring mounting or removal. After further cooling as necessary in theauxiliary station 4, the workpiece 33 is taken out.

In the HIP system of the present invention, a coolant jacket may bemounted around the outer periphery of the vertical pressure-resistantcylinder 7 of the HIP furnace 5 to increase the cooling rate, andsimilar coolant jackets may be mounted around the outer peripheries ofthe vertical cylinders 13 and 13' of the auxiliary stations 4 and 4' tocause a forced circulation of the inside gas. The provision of thesemeans is desirable for improving the function and effect of the methodof the present invention although the equipment cost will be increased.

The lower plug 8 of an improved type used in the present invention willnow be described with reference to FIGS. 1 to 5. As shown in thesefigures, the lower plug of this type comprises an outer annular plug 8awhich holds thereon the hermetic casings 16 and 17, heat insulatingbarrier 10 and heater 9, and an inner plug 8b which is removably fittedin the outer annular plug 8a and which supports the workpiece 33 throughthe heat insulating seat 19 and sample stand 32.

Under such construction, at every loading or unloading of the work it isno longer necessary to remove the treating chamber 11 from the auxiliarystation 4 and then separate the heat insulating barrier 10 from thelower plug 8; in other words, all that is required is only removing theinner plug 8b from the outer plug 8a while the treating chamber isreceived in the auxiliary station 4, and thus operation is extremelyeasy, affording great convenience. Where the lower plug 8 is of such adouble structure, it is preferable in point of design and manufacturethat the inner plug 8b be provided with the lower valve mechanism 23,and this is a matter of course.

FIG. 6 is a schematic vertical section of an HIP apparatus according toanother embodiment of the present invention. In the above embodimentillustrated in FIGS. 1 to 5, the heat insulating barrier 10, heater 9and workpiece 33 can be loaded and unloaded from the lower openings ofthe vertical cylinders 7, 13 and 13' together with the lower plug 8. Onthe other hand, in the embodiment of FIG. 6, the upper plug 6 is removedthereby permitting those portions to be loaded and unloaded from theupper openings of the vertical cylinders 7, 13 and 13'. As shown, a baseplate 42 which serves as a part of the hermetic casing 17 is put on thelower plug 8 through support 41, and the lower end of the hermeticcasing 17 is put on the base plate 42 through a seal ring 43. Further,the valve member 23 for communication and cut-off between the interiorand exterior of the treating chamber 11 is mounted in the base plate 42.In this apparatus, the heat insulating barrier 10, heater 9, workpiece33 and base plate 42 are loaded and unloaded from above the verticalcylinder in an integrally suspended state.

As the heater 9, there is used Ni-Cr wire, Fe-Cr-Al wire, molybdenumwire or graphite, selected according to the temperature used. But,molybdenum and graphite are most preferred from the standpoint ofstability of operation at high temperatures. As the material of thehermetic casings 16, 17 and 20, there is used a gas impermeable materialsuch as stainless steel, heat-resistant superalloy or molybdenum,selected according to the temperature used.

The following is a working example of the method of the presentinvention.

Example

HIP treatment of high speed powder compact was performed using the lowerloading type modular HIP system illustrated in FIGS. 1 to 5. First, inan auxiliary station, the upper and lower valve mechanisms were openedand the internal pressure of the treating chamber was brought to 10⁻¹-10⁻² Torr by vacuum suction, then the interior atmosphere was replacedwith argon gas, followed by a preliminary sintering at 1,000° C. for 1hour in an argon atmosphere.

Then, the upper and lower valves 25 and 25' were closed to seal theargon gas in the treating chamber 11, which was then loaded into the HIPfurnace 5 in a hot condition of the workpiece. Then, the upper valve 25was opened and argon gas was introduced from the conduit 40. At the sametime, the heater 9 was charged with electricity and the internaltemperature and pressure of the treating chamber 11 were raised to1,400° C. and 1,000 atm over a period of 3 hours. While maintaining theinterior of the treating chamber in this state for about 2 hours, therewas performed HIP treatment. Thereafter, the powder supply to the heater9 was turned off and the lower valve 25' was opened to start cooling. Inabout one hour the internal temperature of the HIP furnace was loweredto about 400° C., whereupon pressure reducing and argon gas recoveringoperation was started. The internal pressure was returned to normalpressure over a period of about one hour. At this time, the internaltemperature of the HIP furnace was 290° C. Then, the upper and lowervalves 25 and 25' were closed and the lower plug 8 was taken outtogether with the hermetic casings 16 and 17, heat insulating barrier 10and work 33, and together loaded again into the auxiliary station 4.When the internal temperature was lowered to 200° C., the inner plug 8bwas pulled out together with the workpiece 33. Molybdenum was used asthe material of both the heater 9 and hermetig casings 16 and 17.Heating could be accomplished stadly without sublimation of molybdenumin both the preheating stage and HIP treatment stage, and no substantialoxidation was recognized even after opening to the outside air.

In the method and apparatus of the present invention, as set forthhereinabove, the HIP treatment is performed in the combination of themovable treating chamber 11 with the HIP furnace 5, and after completionof the HIP treatment, rapid cooling is effected by utilization of alarge convective heat conductivity induced by a vigorous convection ofhigh pressure gas, then the treating chamber 11 is taken out from theHIP furnace 5. Consequently, damage and deterioration of the seal ringcaused by opening of the furnace in a state of high temperature, whichis a safety impeding factor, is eliminated completely. Besides, since itis possible to preheat the workpiece 33 in an auxiliary station and loadthe preheated workpiece as enclosed with a predetermined gas atmospherein a hot state into the HIP furnace 5, not only the heat-up time in theHIP furnace 5 is shortened, but also the time of occupying the HIPfurnace 5, especially the time required for lowering temperature, isshortened to a remarkable extent. As a result, the working efficiency ofthe entirety of the modular type HIP system is improved remarkably, andhence not only the cycle time is shortened but also the cooling stepwhich has heretofore been conducted over a long time period in auxiliarystations can be arrived at in an extremely shorter time. Consequently,the number of auxiliary stations for one HIP furnace can be reduced, itis not necessary to use a preheating-dedicated furnace which isexpensive, thus permitting a remarkable reduction of the equipment cost,and the loss of heat energy can be kept to a minimum.

Thus, the method and apparatus of the present invention have variousadvantages. The cycle time in the standard HIP treatment has heretoforebeen 15 hours and 20 minutes, while according to the present inventionit is shortened to 8 hours and 20 minutes only through shortening of thetime period for lowering of the temperature and is remarkably shortenedto 7 hours if preheating is adopted at the same time. Particularly, inthe HIP treatment at a high temperature region of 1,200° C. to 2,000°C., a specially outstanding effect is exhibited, thus greatlycontributing to the improvement of productivity in the HIP treatment.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claim is:
 1. A process for high efficiency hot isostaticpressing in a hot isostatic pressing treatment for sintering ordensifying a ceramic or metallic workpiece in a high temperature andhigh pressure gas atomsphere, which process comprises preheating theworkpiece outside a high pressure vessel prior to said hot isostaticpressing treatment, transferring the preheated workpiece as surroundedwith the gas in a hot state into the high pressure vessel, treating theworkpiece at a high temperature and under a pressure of at least 500 atmin a gas atomsphere, commencing convective cooling of the workpiece withconvective gas at a pressure of at least 500 atm until the temperatureof the workpiece is about 300° C., depressuring the atomsphere withinsaid vessel; and removing the workpiece from said high pressure vessel.